1. Field of the Invention
The present invention relates to a gear shift device for shifting the gear stage in a transmission mechanism.
2. Description of Background Art
At the time of gear shift when a state where a pair of gear trains in a gear transmission mechanism is transmitting power effectively is changed to a state where another gear train is transmitting power effectively, usually a clutch is disengaged to stop power transmission to permit gear shift because resistance is large during power transmission.
Also, when gear shift operation input by a shift pedal directly rotates a shift drum, gear shift operation may not be smooth in such a case as dog engagement trouble; for this reason, a lost motion mechanism is provided between a shift spindle and the shift drum in order to get a good gear shift operation feeling.
A gear shift device with such a lost motion mechanism, which is a constitution for automatically controlling clutch engagement/disengagement, is disclosed in JP-A No. 2008-221410 which was previously filed as a patent application by the same applicant.
In JP-A No. 2008-221410, since the amount of lost motion in the lost motion mechanism varies, a shift regulating mechanism for regulating rotation of the shift drum is provided downstream of the lost motion mechanism.
The shift regulating mechanism restricts rotation downstream of the lost motion mechanism to accumulate the operation force of gear shift operation, and when a sufficient force is accumulated, it removes the restriction to rotate the shift drum by the accumulated force to shift the gear stage, so gear shift operation can be done at a prescribed timing regardless of variation in the amount of lost motion.
Specifically, in the gear shift device described in JP-A No. 2008-221410, a sufficient operation force is accumulated in the lost motion mechanism by pressing the shift pedal forcefully enough and consequently the restriction by the shift regulating mechanism is removed and the shift drum is rotated by the accumulated force so that the shift fork moves the shifter in the gear transmission mechanism and changes the dog clutch connection to perform gear shift or change the speed.
Since gear shift is performed by an accumulated force in the lost motion mechanism as mentioned above, the force accumulated in the lost motion mechanism must be maintained until dog clutch connection change is finished in the gear transmission mechanism; therefore the rider must keep pressing the shift pedal until dog clutch connection change is finished.
Even when the shift pedal is pressed forcefully enough, if the shift pedal is released before completion of dog clutch connection change, the accumulated force in the lost motion mechanism will be lost and no gear shift will be performed.
In JP-A No. 2008-221410, since the lost amount in the lost motion mechanism varies, a shift regulating mechanism for regulating rotation of the shift drum is provided downstream of the lost motion mechanism.
Also, a positioning mechanism (detent mechanism) for determining the position of the shift drum for each gear stage is provided downstream of the lost motion mechanism.
Since this positioning mechanism (detent mechanism) is provided only downstream of the lost motion mechanism or there is no such mechanism upstream of it, as the rider presses the shift pedal, he/she merely feels some resistance produced by compression of a spring but does not feel a click from the detent mechanism and cannot know from a feeling of gear shift operation whether gear shift has been performed or not.
Furthermore, since the gear shift operation force accumulated in the lost motion mechanism varies, the torque of the shift drum cannot be kept optimum.
In addition, in the gear shift device described in JP-A No. 2008-221410, a sufficient operation force is accumulated in the lost motion mechanism by pressing the shift pedal forcefully enough and consequently the restriction by the shift regulating mechanism is removed and the shift drum is rotated by the accumulated force so that the shift fork moves the shifter in the gear transmission mechanism and changes the dog clutch connection to perform gear shift or change the speed.
Since gear shift is performed by an accumulated force in the lost motion mechanism as mentioned above, the force accumulated in the lost motion mechanism must be maintained until dog clutch connection change is finished in the gear transmission mechanism; therefore the rider must keep pressing the shift pedal until dog clutch connection change is finished.
Even when the shift pedal is pressed forcefully enough, if the shift pedal is released before completion of dog clutch connection change, the accumulated force in the lost motion mechanism will be lost and no gear shift will be performed.
Also, in JP-A No. 2008-221410, the rotation angle of the shift spindle is detected and disengagement of the clutch is controlled based on the detected rotation angle.
For the shift spindle on which the rider's gear shift operation works directly, its rotation speed varies depending on the rider and the way of gear shift operation and is not constant.
Therefore, disengagement of the clutch which is based on the rotation angle of the shift spindle and gear shift motion by rotation of the shift drum downstream of the lost motion mechanism do not always take place timely.
If a regulating mechanism for regulating rotation is also provided upstream of the lost motion mechanism for the above reason, means for activating the regulating mechanisms on the upstream and downstream of the lost motion mechanism must be provided and the device may be more complicated because it may be difficult to synchronize both the regulating mechanisms.
The present invention has been made in view of the above problems.
One object thereof is to provide a gear shift device which ensures that gear shift is adequately performed through input of a required level of gear shift operation without continuing the input of gear shift operation, thereby improving operability. Another object of the present invention is to provide a gear shift device which determines the position of a shift drum for each gear stage and enables the rider to feel a click upon gear shift operation input and know whether or not gear shift has been performed, and also keeps the torque of the shift drum optimum.
Another object of the present invention is to provide a gear shift device which, when a required level of gear shift operation is done, changes speed adequately without continuing gear shift operation input and thus improves operability and assures easy synchronization between the upstream and downstream sides of the lost motion mechanism through a simple structure.
Still, another object of the present invention is to provide a gear shift device which ensures smooth gear shift by disengaging the clutch timely for gear shift motion by rotation of the shift drum at any time.